A Battery-to-3.4 V Hybrid Buck-Boost Converter With Always Reduced Conduction Loss

This article presents a hybrid buck-boost converter designed for lithium-ion battery-powered mobile devices. The proposed converter consists of four low-voltage power switches and one flying capacitor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\text {F}}$ </tex-math></inline-formula>). Unlike the conventional buck-boost converters (CBBCs) that employ two power switches in series with an inductor, this converter uses only one. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\text {F}}$ </tex-math></inline-formula>, which is paralleled with the inductor (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i>), facilitates charge transfer to the output capacitor in the buck mode and distributes input current in the boost mode. This configuration significantly reduces inductor current across the entire input voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {IN}}$ </tex-math></inline-formula>) range. By leveraging the low-voltage stress of power switches and reduced current stress of inductor, the conduction loss (CDL) of the power switches is reduced by up to 64% compared with other studies with equivalent silicon areas. The converter was fabricated with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~{\mu }$ </tex-math></inline-formula>m bipolar-CMOS-DMOS (BCD) process using only 5-V devices. Measurement results show that the converter achieves a peak efficiency of 98.6% with a small dc resistance (DCR) of 8 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> and maintains a peak efficiency of 97.3% with a larger DCR of 170 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>. Moreover, the converter achieves an on-die current density of 1.47 A/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>.